Portable signaling systems such as telephone systems utilizing radio links between a portable unit and a base unit connected to the telephone network have been known for some time. As a need for providing privacy in such telephone usage has increased, the infrared band was developed in order to limit the distribution of signals from the portable unit. Such infrared emissions, typically from infrared emitting diodes, were limited to line of sight communications or confined to a single room where infrared reflections from walls and ceilings can extend the range beyond line of sight.
While techniques are known for modulating such infrared emitters, there exists a need for a battery conserving, modulation technique which provides both ample range to the portable unit for convenience and movement about the room as well as battery longevity. In addition, a system is required which couples efficient modulation techniques with a complete system for on- and off-hook control of the system operation in conjunction with conventional keyboard dialing from the portable unit.